The present invention is related to high heat-set efficiency, high unload power spandex and, more particularly, to spandex prepared from a polyether glycol, a mixture of 2,4xe2x80x2-MDI and 4,4xe2x80x2-MDI, and chain extender.
Spandex and spandex-containing fabrics and garments are typically heat-set to provide the fiber or fabric with good dimensional stability and to shape the finished garment. Typical heat-setting temperatures used in commercial operations are 195xc2x0 C. for fabrics containing spandex and 6,6-nylon, 190xc2x0 C. when the fabric contains 6-nylon, and 180xc2x0 C. when the fabric contains cotton. It is desirable to heat-set fabrics containing cotton and spandex, but if the spandex has adequate heat-set efficiency only at temperatures used for nylon-containing fabrics, the spandex cannot be properly heat-set in cotton-containing fabrics, which will be damaged by exposure to the required high temperatures.
A variety of methods has been used to improve the heat-set efficiency of spandex and thereby lower the temperature at which the spandex can be heat-set. For example, the use of 15-32 mole % of 2-methyl-1,5-pentanediamine as a coextender in making spandex is disclosed in U.S. Pat. No. 4,973,647, but such low levels do not provide spandex with sufficiently high heat-set efficiency at the moderate temperatures permitted for fabrics containing cotton. U.S. Pat. Nos. 5,000,899, 5,948,875 and 5,981,686 disclose the use of high proportions of 2-methyl-1,5-pentanediamine and 1,3-diaminopentane chain extender, respectively, to increase the heat-set efficiency of spandex, but making such large changes to the polymer can deleteriously affect fiber properties. U.S. Pat. No. 5,539,037 discloses the use of low concentrations of alkali metal carboxylates and thiocyanate in spandex to increase its heat-set efficiency. However, such salts can be removed by dissolution during fabric processing, and their effectiveness can thereby be reduced.
Japanese Published Patent Application JP7-82608 discloses the incorporation of 3-13 moles of isocyanato-2-[(4xe2x80x2-isocyanatophenyl)methyl]benzene (xe2x80x9c2,4xe2x80x2-MDIxe2x80x9d) with 1-isocyanato-4-[(4xe2x80x2-isocyanatophenyl)methyl]-benzene (xe2x80x9c4,4xe2x80x2-MDIxe2x80x9d) and, further, that at levels above 13 mole % 2,4xe2x80x2-MDI, the properties of the resulting spandex are said to be unacceptable at elevated temperatures.
Japanese Published Patent Applications JP08-020625, JP08-176253, and JP08-176268 and U.S. Pat. Nos. 3,631,138 and 5,879,799 also disclose the use of various levels of 2, 4xe2x80x2-MDI, but the properties of spandex made from such compositions do not have the desired combination of high heat-set efficiency, elongation, and unload power.
There remains a need for improving the heat-set efficiency of spandex.
The spandex of present invention, having a heat-set efficiency at approximately 175-190xc2x0 C. of xe2x89xa785%, is prepared from poly(tetramethylene-co-2-methyltetramethylene ether) glycol, a mixture of 1-isocyanato-4-[(4xe2x80x2-isocyanatophenyl)methyl]benzene (4,4xe2x80x2-MDI) and 23-55 mole %, based on total diisocyanate, of 1-isocyanato-2-[(4xe2x80x2-isocyanatophenyl)methyl] benzene (2,4xe2x80x2-MDI), and at least one chain extender.